A shock mount currently used in the automotive industry to secure truck bodies to truck frames is disclosed in U.S. Pat. Nos. 4,783,039 and 4,720,075 to Peterson et al., the disclosures of which are hereby incorporated by reference. This shock mount has been successful in the industry due to its design features which provide a telescoping metal spacer and metal thimble assembly that snap together to hold the thimble and spacer together until secured with a threaded fastener, and in which the thimble and spacer have mating surfaces to prevent either one from rotating relative to the other, thereby permitting fastening of the threaded fastener with minimal undesirable rotation of one element relative to the other.
While this known shock mount is exceptionally effective and has high strength characteristics, it does not allow for variations in strength requirements. For example, in some instances an automotive or truck manufacturer may specify that the shock mount will not separate in a barrier test, i.e, that the shock mount will not separate when the vehicle in which it is used impacts a barrier at a certain speed. In other instances, the vehicle manufacturer may specify that the shock mount will separate during a barrier test at certain speeds. Such a specification can arise when the vehicle manufacturer is designing crash protection features in which the energy of a crash is dissipated by destruction or separation of various components of the vehicle body. In such case, each shock mount must be separately designed and manufactured, increasing product cost.
These problems were addressed by the shock mount disclosed in U.S. Pat. No. 5,570,867 to Norkus, the disclosure of which is hereby incorporated by reference. This shock mount includes intermitting flanged spacer and thimble members and resilient rings mounted thereto. the thimble is formed from a hollow plastic stem and a metal base. The metal base includes a flange and an internally threaded post. The thimble stem fits over and snaps onto the post. The metal base member is made in either a high strength or low strength configuration. Selection of the appropriate configuration of base member provides a shock mount assembly of the desired separation strength.
While this shock mount design provides excellent results, it suffers from a disadvantage of its own. In order to join the thimble and the spacer together, a plurality of inward protrusions, such as formed on a tabbed washer, are fitted inside the spacer tube so as to engage the tip of the thimble stem when the thimble stem is telescopingly fitted inside the spacer tube. This arrangement requires the manufacture of an additional piece, which consequently adds to the cost of manufacturing the shock mount. Moreover, the provision of inward protrusion may lead to an increased incidence of manufacturing failures, as when the thimble stem is inserted into the spacer tube, one or more of the protrusions may not bend inwardly properly, resulting in a skewed or failed insertion. Furthermore, even if the thimble stem appears to have been inserted properly, the inward protrusions may not properly engage the lip on the thimble stem, thereby lowering the retention force.
What is desired, therefore, is a shock mount assembly which requires less components than known designs, which has a lower cost of manufacture than known designs, which has a lower incidence of manufacturing failures than known designs, and which has a consistently high retention force between components.